1. Field of the Invention
The invention relates to a field emission electron source employing carbon nanotubes.
2. Discussion of Related Art
Carbon nanotubes (CNTs) produced by means of arc discharge between graphite rods were first discovered and reported in an article by Sumio Iijima, entitled “Helical Microtubules of Graphitic Carbon” (Nature, Vol. 354, Nov. 7, 1991, pp. 56-58). CNTs also feature extremely high electrical conductivity, very small diameters (much less than 100 nanometers), large aspect ratios (i.e. length/diameter ratios greater than 1000), and a tip-surface area near the theoretical limit (the smaller the tip-surface area, the more concentrated the electric field, and the greater the field enhancement factor). These features tend to make CNTs ideal candidates for field emission electron sources.
Generally, a field emission electron source having CNTs includes a conductive base, along with CNTs formed on the conductive base. The CNTs act as an emitter of the field emission electron source. The methods adopted for forming the CNTs on the conductive base mainly include mechanical methods and in situ synthesis methods. The mechanical method is performed by respectively placing a single CNT on a conductive base by an atomic force microscope (AFM), subsequently fixing the CNT on the conductive base by conductive or non-conductive adhesives. However, the controllability of the mechanical method is not as desirable because a single CNT is too small in size. As a result, the single CNT will easily be drawn away from the conductive base due to the electric field force. Otherwise, that would damage the field emission electron source and/or decrease its performance.
The in-situ synthesis method is performed by coating metal catalysts on a conductive base and synthesizing CNTs on the conductive base directly by means of chemical vapor deposition (CVD). However, the mechanical connection between the CNTs and the conductive base generally is relatively weak and, thus, unreliable. In use, such CNTs are also easily drawn away from the conductive base due to the electric field force, which would damage the field emission electron source and/or decrease its performance. Furthermore, the shield effect between adjacent CNTs may reduce the field emission efficiency thereof.
What is needed, therefore, is a field emission source with a high field emission efficiency, along with a controllable method for manufacturing the field emission source.